multihulls in ferrocement???

[garrobito]

Hi everybody!
I'll think about multihulls in ferrocement.
What your think about???
Somebody have information about process, add for less weigth and well some actual information??
I have a lot of information about classic system and material, but I thinking have some best; in the last ten years have a lot of changes (for best) whit this system.
thanks you

[gonzo]

I think ferrocement in boat longer than 60' may work. Is this a sailboat or powerboat?

[Tim B]

It's all a question of length, hull beam, forces etc. If you could post some more details, eg. LOA, hull beam, total beam, number of hulls, design speed, intended weight etc. then we can give an opinion... like all yacht design and construction, there's no method that will cover everything.

Cheers,

Tim B.

[Andy]

Nice idea, but I suspect that ferrocement is not going to work very well on a multihull of any size. Key to the performance of a multi is light weight. Even a well engineered ferro structure will weigh about the same as an old plank on frame wood construction, and most weigh a fair bit more! The reason ferro works so well on monohull cruisers is that with heavy displacement the hull weight is proportionately less of the overall displacement than with light displacement, and therefore affects the performance and stability less. With a 'no ballast' multihull, that weight is still there - perhaps even more so as there is more surface area, although creating parts from lighter materials could partly offset this disadvantage. All that said, if you wanted a heavy displacement multi (look at James Wharrams 65' Islander for example), then ferro is an interesting choice. I should point out that I regularly cruise on a ferro monohull, and am a big fan of that boat, so here are some thoughts to consider...

Smaller boats are proportionately heavier than larger boats built in ferro - there is a practical lower limit on hull thickness v strength which penalises small boats.

The materials are cheap, but you need a HUGE and skilled workforce to do the plastering (min. 20 people on a 30 footer) and it MUST be completed in one day. The fitting out costs and time are the same as for any other type of construction, but the boat will be worth less.

Proper materials should be procured and proper procedures adhered to to produce a quality ferro hull. Its easy to get voids and bubbles in the cement which could lead to catastrophic failure late on. The best place to look for guidance on the web about building in ferro is the FAO booklet at http://www.fao.org/docrep/003/v9468e/v9468e00.htm
The Hartley website and owners discussion group should be able to help too.

Lots of fairing will then be required...so the labour is much greater than with many other methods (ok if you have free labour...)

They are easily repaired with basic tools and materials, but many insurers demand professional repairs ($$$'s) and there are very few shipwrights willing to do the work.

They cost more to insure. This is offset by the fact that ferro boats are worth less on the market than other forms of construction so the cheaper valuation means cheaper insurance, often the same as a comparable (but more expensive) fibreglass boat.

The ferro boat I sail on has beautiful classical lines and was finished to a very high standard (much work and $$$$ again), but only the hull is ferro. The rest is traditional wood construction, also very beautiful. The boat is very heavy, with a huge rig and sails, and very satisfying to sail in a freight train kind of way, but very heavy to handle. Last weekend during a cruising muster on the Clyde we were worried that there wasnt enough swinging room in the bay we anchored in, until someone pointed out that if the boats started boucing off each other, we certainly wouldn't have any problems! (Not very courteous or seamanlike, I know...!) Ferro boats are immensely strong, so if cheap materials, strength and outside buildability are on list of priorities, then it could work. But if you want performance, look elsewhere!

And you could use foam packing peanuts for ballast..........The mast could be made of lead, and...........nevermind

[Kevin Lester]

Hi, as a professional concrete technologist and a boating enthusiast I also spent a great deal of time considering ferro cement as a boat building material. I dont believe there have been any advances in the last 10 years that would significantly change the technology or reduce weight. There are a lot of light weight alternatives to sand these days but what you gain in weight loss you loose in strength, and maybe more. Light weight mortar is very weak and far more permeable than the traditional mortar used in ferro cement. I also tried some small projects in ferro cement and found it very difficult to carry out the plastering, while you're plastering one section, the mortar is falling off another section etc, and it's also quite difficult to get a satisfactory surface finish without extensive experience. Once I began to sail on different boats I decided that maximum speed for wind conditions was a primary requirement for me, ferro cement boats take far too much wind to get going for my liking. Concrete technologist or not I eventually decided that the lighter the material, and resultant boat the better for me.

[PAR]

Damn, I hate being the one to say this, but ferro is a reasonable material for hull construction if down and dirty is what your after. Ferro can't be easily inspected as the wire is inside the structure, so a real complete survey would require x-rays, to determine if the wire and rod matrix is any good.

You'll have very little luck with the market in this country as "Samson" children only a mother could love in the early 70's fixed that. Europe is another story, English Windboats Ltd. built a good ferro hull, with the proper sized wire and rod, even Lloyd's approved.

If from a known builder, the ferro boat has a chance of sale there, but not here.

Buy the book "Practical Ferro-Cement Boatbuilding" it is a good volume and describes the correct way to do it.

Weight isn't the real issue in the construction as displacement can be planned for in all craft. Because it's concrete, it doesn't have to be heavy. Boats over 40' can start looking closely at several seemly "heavy" materials for construction.

It's difficult to get a good finish, partly because it has to be done all at once and the skilled labor is still packing the "mud" into the structure as areas are starting to kick off. The plastering is very skilled labor, but the labor force is based in pool construction, where large compound curve shapes are dealt with daily. They don't know a lot about boat hull finishes and there's only so much you can do with the stuff in the time you have to work it.

Personally, if it was my thinking about larger boat construction, I'd be brushing up on my welding skills. Steel is affordable and aluminum is the stuff if you got the cash.